Welders are commonly used in the electronics industry, particularly for welding of sub-miniature components and for wiring of printed circuit boards or other types of circuit connections, for interconnecting packaging panels or circuit boards by discrete wires, or for welding of connector strips of an integrated circuit module or chip to the strip terminals of the substrate which supports the chip. Some of such known welders require that the insulation be stripped from the wire before making a welded connection while others melt the insulation to permit welding of the wire to a terminal or strip. Examples of welders which melt the insulation are shown in U.S. Pat. Nos. 3,263,059 and 3,384,958. An example of a welder in which the insulation must be previously stripped from the wire is found in U.S. Pat. No. 3,333,083. In each of the welders, one electrode is placed in contact with the wire to be welded while a second electrode is connected to the terminal or strip to which the wire is to be welded to complete the circuit. The second electrode is generally spaced from and nonparallel to the first electrode and may contact the terminal or strip at any point thereon. In U.S. Pat. No. 3,459,918, a welder is disclosed in which the electrodes are both disposed on one side of the element to be welded but in which there is no provision for removal of insulation from the wire.
None of the above described welders are capable of welding an insulated wire to a terminal or strip rapidly and in an automated fashion. An automatic soldering assembly is disclosed in U.S. Pat. No. 3,840,169, but the apparatus disclosed in this patent requires two independently controlled, non-parallel electrodes to complete the circuit to bond the wire to the circuit board, and is not suitable for automated, rapid welding procedures. An automated welder is disclosed in U.S. Pat. No. 3,278,717, but this welder has electrodes disposed on opposite sides of the elements to be welded and there is no provision for removal of insulation from the wire. When such welders having opposed, spaced electrodes are used in circuit board applications, the electrodes must be placed on opposite sides of the board. This arrangement requires the use of plated-through holes, which is not always desired. Also, such holes sometimes produce incomplete electical connections due to defects in the plating, and thus unacceptable welds can result.